Heretofore, photographic processes using silver halide have most widely been practiced, since they provide excellent sensitivity, gradation, and like photographic properties as compared with, for example, electrophotographic processes and diazo type photographic processes.
In recent years, techniques have been developed with silver halide light-sensitive materials which provide images simply and in a short time by employing dry processing which involves heating in place of the conventional wet processing which involves development in a developing solution. Heat developable light-sensitive materials are known in the art, and heat developable light-sensitive materials and the process thereof are described in, for example, Shashin Kohgaku no Kiso, pp. 553-555 (published by Corona Co., Ltd.), Eizoh Johhoh, April, 1978, p. 40, Nebletts Handbook of Photography and Reprography, 7th Ed. (Van Nostrand Reinhold Company), pp. 32-33, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, 3,457,075, British Pat. Nos. 1,131,108, 1,167,777, and Research Disclosure, RD-17029, pp. 9-15 (June, 1978).
Many processes have been proposed for obtaining color images. As to a process of forming color image by binding an oxidation product of a developing agent with a coupler, U.S. Pat. No. 3,531,286 proposes p-phenylenediamine type reducing agents and phenolic or active methylene couplers, U.S. Pat. No. 3,761,270 proposes p-aminophenol type reducing agents, British Patent No. 802,519 and Research Disclosure, pp. 31 and 32 (September, 1975) propose sulfonamidophenol type reducing agents, and U.S. Pat. No. 4,021,240 proposes a combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler.
However, these processes have the disadvantage that, since an image of reduced silver and a color image are simultaneously formed in exposure areas upon heat development, the color image becomes turbid. As a means for removing this disadvantage, the silver image is removed by a liquid treatment, or the dye alone is transferred to a sheet having another layer, for example, image receiving layer. However, it is not easy to discriminate an unreacted material from a dye and only transfer the dye.
As to a process of forming positive color image according to a light-sensitive silver dye bleach process, useful dyes and bleaching processes are described in, for example, Research Disclosure, RD-14433, pp. 30-32 (April, 1976), ibid., RD-15227, pp. 14-15 (December, 1976), and U.S. Pat. No. 4,235,957.
In these processes, however, an additional step and an additional material are necessary for heating the materials with an activator sheet for accelerating bleaching of the dye superposed on them, and the resulting dye image suffers gradual reductive bleaching during a long term storage with the copresent free silver or the like.
Further, the above-described processes generally require a comparatively long developing time, and provide images having serious fog and low image density.
In order to overcome these disadvantages, there has been disclosed an image forming process based on heat development utilizing a compound having a dye moiety and being capable of releasing a mobile dye at elevated temperatures corresponding to or inversely corresponding to reduction of silver halide to siver (hereinafter, dye providing substance). For example, this process is disclosed in Published Unexamined European Pat. Nos. 76,492 and 79,056, Japanese Patent Application Nos. 28928/83 and 26008/83 (corresponding to European Pat. No. 120,306).
These systems have removed the above-described disadvantages to some extent but, when color sensitized silver halide is used therein, there arises deterioration of preservability of the light-sensitive materials. This may be attributed to the fact that, since the dye providing substance itself has a dye moiety, the dye properties of the dye moiety cause a mutual action, when used together with silver halide which has been color sensitized with a sensitizing dye, with the sensitizing dye adsorbed on the silver halide grains. Thus, the adsorbed sensitizing dye being desorbed from the surface of the silver halide grains during storage.
The above-described disadvantage is fatal with color light-sensitive materials.